Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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This invention relates to gate valves. In particular, this
invention relates to gate valves which have a wedge-shaped valve
member and which include an internal pressure equalizing valve for
use in reducing the pressure differential between the upstream and
downstream sides of the wedge-shaped valve member prior to opening
of the gate valve.
PRIOR ART
A wedge-shaped gate valve which incorporates a pressure
equalizing valve is disclosed in French Patent No. 368,879, October
22, 1906 issued to M. Perrin. In this structure, the pressure
equalizing valve is in the form of a ball. When the valve stem is
cracked open, the ball will be raised from the valve seat to permit
fluid to flow from the upstream side to the downstream side of the
valve. The chamber in which the ball is housed will become flooded
with the fluid passing through the pressure equalizing passage and
this pressure buildup will tend to move the ball towards the closed
position closing off the through passage. This pressure buildup
within the chamber above the ball valve will cause the ball valve to
"chatter" even when the gate valve is moved to its opened position.
German Patent No. 52747, Carl Giebeler, dated October 5,
1887 is directed to a gate valve in which the pressure valve is
threadedly mounted on the main valve stem. The pressure equalizing
valve cannot be moved relative to tne valve stem without rotating
the valve stem.
The present invention provides a wedge type gate valve in
which the pressure equalizing valve is located in a chamber in the
valve member which is vented to the downstream side of the gate to
prevent a buildup of pressure which would cause the pressure
equalizing valve to move to a closed position.
The vent passage which opens from the pressure equalizing
valve chamber to the downstream side of the gate also permits a
buildup of pressure in the pressure equalizing valve chamber which
will prevent opening of the pressure equalizing valve when the
pressure on the downstream side of the valve exceeds the pressure on
the upstream side of the valve.
It is an object of the present invention to provide a
simple and efficient pressure equalizing valve in a wedge-shaped
valve member of a gate valve which will open freely when the
pressure on the upstream side exceeds the pressure on the downstream
side and the valve stem is cracked open.
It is a further object of the present invention to form the
discharge of the pressure equalizing passage which opens towards the
downstream side so as to generate sonic velocity in the discharging
stream of gates at the normal working pressures.
According to one aspect of the present invention, there is
provided in a gate valve having a valve stem mounted in a
wedge-shaped valve member for limited relative movement betwelen an
extended position and a contracted position, said wedge-shaped valve
member having a pressure equalizing passage opening there through
which communicates between the upstream and downstream sides
thereof, a pressure equalizing valve located in a chamber formed in
said valve member which is arranged to communicate with said through
passage, said pressure equalizing valve being movable toward and
away from a valve seat located in said pressure equalizing passage
to close and open the pressure equalizing passage, said chamber
being proportioned to provide an expansion compartment on the side
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of the pressure equalizing valve remote from the valve seat to
accommodate movement of the pressure equalizing valve from the
closed position to the opened position, said pressure equalizing
valve being freely movable within said chamber when said valve stem
is in said extended position relative to said valve member, the
improvement of a vent passage opening from said expansion
compartment to said chamber through the downstream side of the valve
member such that any pressure buildup in the expansion compartment
resulting from the opening of the pressure equalizing valve may be
vented to the downstream side of the valve member and will not cause
the pressure equalizing valve to move to its closed position.
The invention will be more clearly understood after
reference to the following detailed specification read in
conjunction with the drawings wherein;
Figure 1 is a sectioned pictorial side view of a gate valve
constructed in accordance with an embodiment of the present
invention showing the pressure equalizing valve in the closed
position,
Figure 2 is a view similar to Figure 1 showing the pressure
equalizing valve in the open position,
Figure 3 is a cross-sectional side view showing the
pressure equalizing valve in a partially opened position;, and
Figure 4 is an exploded view of the components of the
pressure equalizing valve.
With reference to Figure 1 of the drawings, the reference
numeral 10 refers generally to a gate valve constructed in
accordance with an embodiment of the present invention. The valve
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10 consists of a body 12 which has a through passage 14 which
includes an upstream section l6 and a downstream section 18, a
wedge-shaped gate valve member 20 is slidably mounted in the housing
12 and a valve stem 22 is provided for raising and lowering the gate
valve.
Gate valves of this general type are well known and
consequently, the structural features of the valve WL11 not be
described in detail.
The wedge-shaped gate valve member 20 has an upstream face
24 and a downstream face 26 directed toward the upstream section 16
and downstream section 18 of the through passage 14 respectively.
The gate valve member 20 is formed with a pressure equalizing
passage generally identi~ied by the reference numeral 28 which
extends from the upstream face 24 to the downstream face 26. The
pressure equalizing passage 28 includes an input passage 30 which
extends inwardly from the upstream face 24 to axial se~tion 32. The
axial section 32 opens through a replaceable valve seat insert 34
into a chàmber 36. The pressure equalizing passage 28 is completed
by an outlet 38 which opens into the downstream section 18. i~
cone-shaped valve seat 40 is formed in the insert 34. A collar 42
is threadedly mounted in the upper end of the chamber 36 and has a
slip~ay passage 44 which opens axially therethrough. A pressure
equalizing valve 46 is mounted in the chamber 36 in a free-fitting
sliding relationship. The pressure equalizing valve 46 has a head
portion 48 and a stem portion 50. The head portion 48 has a
cone-shaped end 52 which will fit in a fluid-tight face-to-face
relationship with the cone-shaped valve seat 40 in use. The head
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portion ~8 is proportioned so as to fit in a free-fitting sliding
relationship in the chamber 36 and as a result, a narrow annular gap
52 is provided between the head portion 48 and the side wall 54 of
the chamber 36. This gap is sufficiently large to permit the fluid
passing through the pressure equalizing passage 28 to fill the
chamber 36 above the head portion 480 The stem portion 50 of the
pressure equalizing valve is proportioned to ~it in a free-fitting
sliding relationship within the slipway passage 44. The head
portion 48 is proportioned so that an expansion compartment 56 will
be formed in the chamber 36 above the head portion when the head
portion is seated on the valve seat. The expansion compartment 56
is proportioned to permit the movement of the head portion 52 away
from the`valve seat to a sufficient extent to permit full flow of
fluids through the pressure equalizing passage 28. A vent passage
58 opens from the expansion compartment 56 through the downstream
side of the valve member such that any pressure buildup in the
expansion chamber resulting from the opening of the pressure
equalizing valve may be vented to the downstream side 18.
The valve stem 22 has a T-shaped head porti~n 60 mounted in
a complimentary notch 62 formed in the upper end of the valve member
20. The head 60 is smaller than the notch 62 so that it can be
axially moved relative to the gate valve member 20 without causing
movement of the gate valve member 20. This permits movement of the
head portion 60 between a position in which it will bare against the
stem portion 50 o~ the pressure equalizing valve ~6 to seat the
pressure equalizing valve in a position closing the through
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passage. In addition, the stem can be 7'cracked open" to provide a
gap between the head 60 and the stem portion 50 of the pressure
equalizing valve to permit opening of the pressure equalizing valve
before the valve stem 22 engages the gate valve member 20.
It will be noted that the outlet 38 of the pressure
equalizing passage 28 is longitudinally spaced with respect to the
vent passage 58 in the direction of movement of the pressure
equalizing valve 46. When the pressure equalizing valve 48 is
seated in a position closing the through passage, the cone-shaped
end of the pressure equalizing valve will be lGcated on the side of
the outlet 38 remote from the vent passage 58. As a result, any
pressure which builds up in the downstream portion 18 can only be
a~plied to the compartment 56 through the vent passage 58 and will
therefore be effective in preventing opening of the pressure
e~ualizing valve 46.
When the fluid which is to be controlled by the gate valve
is a gas, the outlet 38 of the pressure equalizing passage is
preferably formed as a nozzle so as to generate a discharging stream
of gas at a sonic velocity into the downstream section 18 resulting
rom the normal pressure differential between the upstream side 16
and the downstream side 18 in the environment in which the valve is
to be used. By generating a discharging stream at sonic velocity,
the reaction forces will be applied in a series of shock waves to
the wedge-shaped gate valve member and these shock waves will
~acilitate the opening of the wedge-shaped gate valve member when
the handle 8 is rotated to open the gate valve member in use.
In use! when the valve member is positioned in the closed
position illustrated in Figures 2 and 3 of the drawings, the gate
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valve member 20 closes the through passage 14 and the vent passage
~8 communicates with the compartment 56. When the valve is to be
opened, the handle 8 is rotated to raise the T-shaped head portion
60 of the stem away from the stem portion 50 of the pressure relieve
valve until it comes in contact with the shoulders 64 o~ the notch
62. If the fluid pressure in the upstream section 16 is greater
than the fluid pressure in the downstream section 18, the pressure
applied by the fluid on the upstream side to the underside of the
pressure equalizing valve 46 will cause the pressure equalizing
valve 46 to move within the chamber 36 from the closed position to
the opened position, thus opening the pressure equalizing passage
28. If the pressure differential between the upstream section 16
and downstream section 18 is sufficient, the velocity of the stream
of gaseous fluid which is discharged through the outlet 38 will be
sonic velocity and this will serve to generate shock waves which
will be applied to the downstream face 26 of the gate valve member
which will serve to facilitate the subsequent movement of the gate
valve toward the open position in response to ~urther rotation of
the handle 8. When the pressure e~ualizing valve 46 moves to an
open position, the fluid passing through the pressure equalizing
passage 28 will flood the chamber 36. The fluid pressure in the
chamber 36 will not, however, exceed the fluid pressure in the
pressure equalizing passage 28 because the vent passage 58 will
permit venting of the chamber 36 to the downstream section 18.
Consequently, the pressure in the compartment 56 will always be less
than the opening pressure applied to the pressure equalizing valve
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46 by the fluid in the pressure equalizing passage 28 when the
pressure in the upstream 16 is greater than the pressure in the
downstream 18. If, however, the pressure in the downstream section
should increase to the point where it is greater than the pressure
in the upstream section, the pressure equalizing valve 46 be caused
to act as a check valve and will close the through passage 38. This
results from the fact that the pressure in the downstream section 18
can be transmitted to the fluid in the compartment 56 through the
vent passage 58 and when the pressure in the compartment 56 exceeds
the pressure in the pressure equalizing passage 36, the pressure
equalizing valve 46 will move to a closed position bearing against
the valve seat 40. This movement of the pressure equaliz;ng valve
will be independent of the movement of the valve stem 22. Thus it
will be seen that the pressure equalizing valve not only serves to
reduce the pressure differential between the upstream and downstream
sides Oe the valve when the upstream is the high pressure side, but
also serves to prevent fluid flow through the pressure equalizing
valve in circumstances where the pressure on the upstream section 16
is greater than the pressure in the downstream section 18. The fact
that the pressure equalizing valve 46 will not open in circumstances
where the pressure in the downstream section is greater than the
pressure in the upstream section can be helpful in many practical
situations because it will make the opening of the valve much more
difficult in these circumstances and this can provide a warning to
the operator that the pressure conditions in the system in which the
valve is installed are not the normal operating conditions.
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Various modifications of the present invention will be
apparent to those skilled in the art without departing from the
scope of the invention.
In one such modification, a plurality of outlets 38 are
formed in the downstream wall of the gate valve, each opening from
the chamber 36.
